In the above context, various types of apparatus are known, among which (without limitation) may be cited the following:                position lights of low intensity and short range;        short range, passing or dipped beam headlights, of greater intensity and with a longer range, covering approximately 70 meters of the road ahead and used essentially at night, the distribution of their light beams being such that it avoids dazzling the driver of a vehicle travelling in the opposite direction;        long range or main beam headlights, and long range complementary driving lights, having a zone of vision over the road of approximately 200 meters; these lights must be extinguished when passing another vehicle, in order not to dazzle its driver;        improved headlights of the so-called dual-function type which combine the functions of passing lights and main beam lights, by incorporating a removable screen;        anti-fog headlights, or foglights;        stop lights; and        direction indicators.        
The combination, according to the invention, of a light emitting element with a complementary module may be obtained with any one of these devices whatever. The complementary module may in this connection for example contain an electronic circuit board of the light control system (LCS) type which serves to produce the so-called complex functions (FBL, DBL, ERL, Cordy and so on) for the apparatus with which the said electronic circuit board is associated. The complementary module may also include a control circuit board for governing a mechanical element of the actuator type. Nevertheless, the invention will be described more particularly with reference to a headlight apparatus of the passing beam type with a complementary module of the ballast type.
In the context of the invention, a ballast is a particular complementary module which is preferably contained in a headlight apparatus of the passing beam type which uses a discharge lamp as its light source. More particularly, in the invention, reference is made to ballasts of the high intensity discharge (HID) type, which are necessary in order to create and maintain an electric arc used in xenon lamps. An electronic module produces a high voltage in the ballast in order to obtain the electrical arc in the light source which is used. In this type of headlight, a complementary module of the ballast type is therefore indispensable in order to provide the energy which is necessary for proper operation of the headlight.
However, integration of such a module into the interior of the headlight apparatus must have regard to a number of constraints, namely the following:                it must be done by means of as simple as possible an assembly operation;        it must occupy little space;        in order to prevent any damage to the elements contained within the ballast, it must have regard to the high temperatures which can occur in operation of the headlight apparatus;        it must take into account the need for transmissions of electrical signals between the various elements of the headlight apparatus; and        the association between the headlight element and the complementary module must not give rise to sealing problems in respect of either one of these components.        
In the current state of the art, it has in particular been proposed to provide a headlight apparatus which does attempt to have regard to these various constraints. Such a headlight apparatus is shown diagrammatically in FIG. 1 of the accompanying drawings.
In FIG. 1 a headlight apparatus 100 consists essentially of a headlight element 101 and a ballast 102 of the HID type. In the headlight element 101 there is, in particular, a reflector 106 in which a light source 103, of the discharge lamp type, is placed. The light source 103 produces a light beam which passes out of the headlight element 101 at the level of an output surface 108 which constitutes the front part of the headlight element 101. The light source 103, which rests on a lampholder element 104, is connected to a high tension module 105 which supplies power to it.
The high tension module is energised by means of a first electrical link 107 constituting an input lead, which is preferably screened and which passes out of the headlight element 101 at the level of a first aperture formed in a lower face 109 of the headlight element 101, in which a first connector receiving element 110 is located. This first receiving element 110 is adapted to receive a first connector 111 of the ballast 102. The latter includes a second connector 112 which is associated with a second connector receiving element 113 disposed at the level of a second aperture formed in the lower face 109 of the headlight element 101. A second electrical link 117, constituting an output lead, is connected to the second connector 112; it enables various electrical signals to be carried, in particular a power supply signal for the ballast and various control signals coming from the vehicle. Accordingly, the term “lead” as used in this description and the claims, is to be understood to mean a bundle or other connector consisting of one or more electrical conductors.
Fastening between the ballast 102 and the headlight element 101 is obtained between the lower face 109 of the headlight element 101 and an upper face 115 of the ballast 102, at the level of an aperture 114 which is formed in at least part of the lower face and of the rear face of the headlight element 101, that is to say approximately under the assembly that consists of the reflector 106, lampholder element 104, and high tension module 105. The ballast 102 is fixed on the headlight element 101 by means of at least two screws 116, which are disposed vertically in holes provided for this purpose.
The choice of the arrangement of the ballast 102 is made, in particular, by considering the least hot zone of the headlight apparatus. Generally, this zone corresponds to the zone which is situated below the reflector element 101, which is also quite accessible and in consequence facilitates assembly. It is at this point that the heat produced by the light source 103 is least severe, and the lower portion of the headlight element 101 is easier of access than, for example, the rear portion.
In the invention, assembly of the headlight element and complementary module together, as just described, does have a certain number of disadvantages, namely the following. To start with, the fact that the connector receiving elements 110 and 113 are disposed vertically on the rear face 109 of the headlight element 101 poses a first problem. This is that the mould in which the headlight element 101 is made is open in a horizontal direction, and the need to be able to dispose the connector receiving elements in vertical positions makes it necessary to provide drawers in the mould used. Since this mould is used for the assembly of headlight elements including those which operate with a light source of the halogen type, this disadvantage, besides imposing a penalty in terms of complexity in manufacture of the mould, involves an undesirable increase in the cost of assembly of the headlight elements.
The presence of two connectors is also a problem in itself. In this connection, the more connectors are provided, the more delicate is the assembly operation and the longer it takes to perform.
A third problem encountered with headlight apparatus in the state of the art, when associated with a complementary module, is that they are relatively large, the complementary module 102 having a substantial height because of the way in which it is designed.
A fourth problem met with in headlight apparatus in the state of the art, when associated with a complementary module, lies in the complexity of the assembly operation, in particular by reason of the fastening means employed. In the state of the art as described above, it is necessary to make use of at least two screws to secure together the headlight element 101 and the ballast 102. The fewer screws there are, the shorter will be the time taken for assembly and the simpler will be the assembly operation.